1. Field of the Invention
The present invention relates to a method for a liquid crystal display device (LCD) and a method for manufacturing the same, more particularly to an LCD device having enhanced connection stability between a driving circuit of the LCD device and chip on glass (COG), a chip on film (COF) or a flexible printed circuit film (FPC) and a method for manufacturing the same.
2. Description of the Related Art
In the information society of the present time, electronic display devices are more important as information transmission media and various electronic display devices are widely applied for industrial apparatus or home appliances. Such electronic display devices are being continuously improved to have new appropriate functions for various demands of the information society.
In general, electronic display devices display and transmit various pieces of information to users who utilize such information. That is, the electronic display devices convert electric information signals outputted from an electronic apparatus into light information signals recognized by users through their eyes.
The electronic display devices are generally divided into emissive display devices and non-emissive display devices. The emissive display devices display light information signals through emitting lights and the non-emissive display device displays the light information signals through reflection, a scattering or an interference. The emissive display devices include a cathode ray tube (CRT), a plasma display panel (PDP), a light emitting diode (LED) and an electroluminescent display (ELD). The emissive display devices are called as active display devices. Also, the non-emissive display devices, called as passive display devices, includes a liquid crystal display (LCD), an electrochemical display (ECD) and an electrophoretic image display (EPID).
The CRT has been used for television sets or computer monitors as the display device for a long time since it has a high quality and a low manufacturing cost. The CRT, however, has some disadvantages such as a heavy weight, a large volume and high power dissipation. For these reasons, recently the demand for new electronic display devices has been greatly increased, such as a flat panel display device which has excellent characteristics, for example, a thin thickness, a light weight, a low driving voltage and a low power consumption. Such flat panel display devices can be manufactured using the rapidly improving semiconductor technology.
In the flat panel devices, liquid crystal display (LCD) devices have been widely utilized for various electronic devices because the LCD devices are thin, and has low power dissipation and high display qualities approximately identical to those of the CRT. Also, the LCD device can operate under a low driving voltage and can be easily manufactured.
The LCD devices are generally divided into a transmissive type and a reflection type. The transmissive type LCD device displays information by using an external light source and the reflection type LCD device displays information by using ambient light. The manufacturing processes for the trasmissive or the reflection type LCD device are already disclosed in various literatures.
FIGS. 1A, 1B and 1C depict the cross-sectional views of a conventional method for manufacturing a LCD device.
Referring to FIG. 1A, after a metal layer such as an aluminum (Al) layer or a chrome (Cr) layer is formed on a substrate 10 composed of an insulating material, the metal layer is patterned to form a gate electrode 15 and a gate pad 20. Then, a gate insulation layer 25 is formed on the whole surface of the substrate 10 where the gate insulation layer 25 formed by depositing silicon nitride and by a plasma chemical vapor deposition method.
Subsequently, amorphous silicon and an in-situ doped n+ amorphous silicon are formed on the gate insulation layer 25 and are patterned and an amorphous silicon layer 30 and an ohmic contact layer 35 are formed on the gate electrode 15.
Then, a metal such as molybdenum (Mo), aluminum, chrome or tungsten (W) is deposited on the gate electrode 15 and patterned to form a source electrode 40 and a drain electrode 45. Hence, a thin film transistor (TFT) 60 having the gate electrode 15, the amorphous silicon layer 30, the ohmic contact layer 35, the source electrode 40 and the drain electrode 45 is formed in an active region 50 of the substrate 10 besides a pad region 70 of the substrate 10 corresponding to a peripheral portion of the active region 50.
Referring to FIG. 1B, an organic insulation layer 75 composed of an organic resist is formed on the active and the pad regions 50 and 70 of the substrate 10 so that a lower substrate of the LCD device is completed.
With reference to FIG. 1C, a mask (not shown) is positioned over the organic insulation layer 75 in order to from a contact hole 80 and a pad opening 81. Then, the contact hole 80 exposing the drain electrode 45 is formed in the organic insulating layer 75 after the organic insulation layer 75 is exposed and developed by using the mask. In this case, the pad opening 81 partially exposing the gate pad 20 is formed in the pad region 70 by simultaneously removing the gate insulation layer 25 under the organic insulation layer 75.
Subsequently, after a metal having an excellent reflectivity such as aluminum or nickel (Ni) is coated in the contact hole 80 and on the organic insulation layer 75, the metal is patterned to form a reflection electrode 85 having a predetermined shape of a pixel. At that time, a pad electrode 86 is formed in the pad opening 81 and on the organic insulation layer 75 positioned a peripheral portion of the pad opening 81 in the pad region 70.
Then, an orientation layer is formed on the resultant structure and an upper substrate (not shown) corresponding the lower substrate is prepared. The upper substrate includes a color filter, a transparent electrode and an orientation layer. Continuously, several spacers are interposed between the upper substrate and the lower substrate to combine the upper substrate with the lower substrate and a liquid crystal layer is formed between the upper substrate with the lower substrate, thereby accomplishing the LCD device.
In order to apply a driving signal to the LCD device from outside, a chip on glass (COG), chip on film (COF) or flexible printed circuit film (FPC) is connected to the LCD device as a connection device.
In the conventional method for manufacturing the LCD device, however, since the organic insulation layer or a layer having thick thickness is formed on the TFT as a protection layer, the connection failure between an external device and the LCD device may occur due to the step between the pad region having the metal formed thereunder and the peripheral region when the external device such as the COG, the COF or the FPC is connected to the pad region of the LCD device.
FIG. 2 is a cross-sectional view for showing the external device connected to the pad region of the LCD device in FIG. 1C. Referring to FIG. 2, the opening 81 is formed by exposing and developing the organic insulation layer 75 after the organic insulation layer 75 is coated on the pad region 70 including the pad 20, and then the pad electrode 86 is formed in the opening 81 and on a portion of the organic insulation layer 75 positioned near the opening 81.
Subsequently, in order to combine the pad electrode 86 with the COG or the COF, output ends of the COG or the COF or bumps 94 of input portion of the COG or the COF are aligned with the pad electrode 86 after an anisotropic conductive film 90 having conductive balls 92 is positioned on the pad electrode 86. Continuously, the pad electrode 86 and the bumps 94 are electrically connected to each other through the conductive balls 92 by a compression process.
The organic insulation layer 75 coated on the pad region 70 is formed thick enough to protect the TFT and to form the reflection electrode 85. This creates a high step of about 3 to 4 μm between one portion of the pad region 70 where the pad 20 is positioned and the other portion of the pad region 70. When the COG or the COF is connected to such pad region 70 by the compression process, the connection between the pad 20 and the COG or the COF may fail in the pad opening 81 due to the step in the pad region 70 as shown in FIG. 2. Thus, the LCD device module may not operate or operate improperly due to the connection failure.
In particular, the connection failure between the COG and the pad may be increased since the COG is connected to the pad by using the conductive ball with a diameter of about 5 μm during the conventional compression process.
Also, electrical shorts between adjacent pads become more likely may be increased when the organic insulation layer formed on the pads and the peripheral region is removed because the organic insulation layer prevents the electrical short between the adjacent pads among a plurality of pads, whereby reducing the reliability of the product. Therefore, the organic insulation layer positioned around the pad should be not removed.